Temperature regulating system



May 24, 1938.

F. w. HOTTENROTH, Jl

TEMPERATURE REGULATING SYSTEM Filed June 30, 1936 Fig.1.

Fig.2.

Inventor:

His Attorneg.

Patented May 24, 1938 TEMPERATURE REGULATING SYSTEM Frederick W.Hottenroth, In, y Mass assignor to General Electric Company, a corporation of New York Application June so, 1936, Serial No. aamof 5 Claims.(01. 236-68) My invention relates to a new and improved temperatureregulating system for controlling the operation of temperature changingmeans to maintain predetermined temperatures within a desired region.More particularly my invention relates to improvements in systems inwhich the thermal responsive means controlling the temperature changingmeans is influenced by a local source'of heat to change the time ofcontrol.

Systems of the above type, although widely used, are open to theobjection that they are deleteriously affected by voltage fluctuationsin. the source from which they derive their energy. The voltagefluctuation and the difference from rated voltage in some distributionnetworks are as much as plus or minus 10 per cent of the rated voltage.Since the heat generated in the thermal element of the system varies asthe square of the voltage the fluctuations noticeably disturb normaloperation.

It is, therefore, a primary object of my invention to provide means tocompensate for the effect of voltage fluctuations upon the temperatureregulating system. According to my invention I accomplish this byconstructing the thermal responsive means of two bimetallic stripshaving different electrical resistancesfastened at their ends to form asingle unitary element. The main element, corresponding to the usualthermostat, is constructed of relatively low resistance material andlarge cross-sectional area so that it is responsive to changes intemperature of the magnitude normally occurring in the region in whichit is placed but, because of its relatively low resistance and largecross-sectional area, will not respond to any great extent to variationsin current flow therethrough. The auxiliary element is constructed of arelatively thinner and narrower strip and, preferably of higherresistance material, so that it has a relatively smaller cross sectionalarea than the main element and is so mounted with respect to the latterthat the two move in opposite directions in response to temperaturevariations. The auxiliary element is also made considerably shorter thanthe main element so that it will not respond appreciably to variationsin an ambient. It will, however, respond readily to variations incurrent flow. Thus, the smaller strip is not affected by ambient but isaffected by current flow and the larger strip is afl'ected by ambientbut not by current flow.

Where an ordinary bimetallic strip is cooperatively associated with asingle contact an infln'itestimal temperature change will open and closethe contacts. In an arrangement consisting of two inversely mountedbimetallic strips a definite temperature change is, necessary betweenthe opening and the closing of the contacts. When the contacts close, acurrent dependent upon the value of the voltage passes through bothbimetallic strips. It is obvious, therefore, that variations in currentflow due to voltage fluctuations will result in a variation inthe temperature diflerential necessary to effect opening and closing of thecontacts. However, the addi- -tion of an electrical heating coil toprovide the local source of heat compensates for any voltagefluctuations because an increase in current, while it will increase thetemperature differential necessary to open the contact, will alsoincrease the heating eifect of the local source and thereby decrease thetemperature diflerential necessary to open the contacts. Thus, byproperly proportioning the two bimetallic elements and the heating coilthe changes resulting from fluctuations in voltage may be madecompensatory.

Other objects, purposes, and characteristic features of the inventionwill in part be pointed out hereafter and will in part be apparent fromthe description and accompanying drawing. In describing the invention indetail, reference will be made to the accompanying drawing in which:

Fig. 1 shows a diagrammatic representation of one embodiment of thepresent invention; and Fig. 2 shows a perspective view of the thermalresponsive element used in the embodiment of Fig. 1.

Reference numeral Ill represents a space or region such as a building,room or the like that is to be supplied with a heat exchange medium tomaintain the temperature conditions therein within predetermined limits.The heat exchange medium, which in the present embodiment is illustratedas being either steam or hot water, is supplied to a radiator H underthe control of a manually operable valve l2 placed in an inlet conduit I3 leading to the" aforementioned radiator from a suitable source ofsteam or hot water such as a furnace H. A return conduit I! for thesteam or hot water also leads from the radiator II to the furnace. Thefurnace. illustrated as being an oil furnace 0! any usual construction,is provided with an electric motor i8 adapted to be energized in orderto increase the intensity of the source of heat. The term intensity ofthe source of heat" is herein used generically to indicate not only asystem in which combustion takes place intermittently but also toinclude systems in which combustion is continuous but the rate thereofmay be varied, as by the operation of dampers.

Energy is supplied to the motor from a suitable source |I whenever thetemperature within the space l0 decreases below a predetermined value.In such event, a thermal responsive means indicated generally byreference numeral l8 and consisting of a main bimetallic element l9 andan auxuliary bimetallic element 20 is adapted to close a circuit acrosscontacts 2| and 22 to energize a relay 26 controlling the operation ofthe burner motor through a circuit that is as follows: conductor 23, alocal source of heat or preheat coil 24, rriain bimetallic element l9,auxiliary bimetallic element 20, contacts 2| and 22 in engagement,conductor 25, and relay 26. When energized relay 26 actuates itsassociated switch 21 upwardly to close a circuit from the supply I! tothe motor l6.

Construction of the thermal responsive means I8 is illustrated moreclearly in Fig. 2. It will be noted from this figure that the mainelement I9 is considerably longer, wider and thinner than element 20 andit may be, and preferably is, constructed of material having a lowerresistance than the latter element. The element |9 is suitably mountedupon a stationary member 28 and contact 22 is adjustably mounted upon asecond stationary member 29. .As previously stated, the bimetallicelements are -mounted for inverse movement, i. e.', the elements move inopposite directions in response to any given temperature variation.Element I9 is preferably constructed of materials having differentcoefiicients of expansion and in the figure section |9a may be made ofinvar and section |9b of brass. Similarly, element 20 may be constructedof the same materials with the exception that 20a is made of invar and20b of brass. The two parts may be fastened end to end by rivets 30 orby any other suitable means.

Before considering the description of operation, it may be well to pointout that the main bimetallic element I9 is relatively wide and thick andas a result has a considerable cross section area so that it is notgreatly responsive to variations in current flow therethrough. However,it is responsive to variations in ambient in the same manner as theusual bimetallic element of any thermal responsive means. On the otherhand, the auxiliary bimetallic element or strip 20 is short, narrow, andthin, and, consequently, has a high resistance. It is therefore,responsive to changes in current flow but, on. the other hand, is notresponsive to changes in ambient because of its short length. The properratio of cross section area of the two elements depends upon theelectrical resistance of the materials used and may be determinedaccordingly.

Whenever the temperature within space In decreases below a predeterminedvalue, contacts 2| and 22 close the previously described circuit toenergize relay 26. The burner motor 5 is energized and space In issupplied with heat from the source |4. Whenever the temperature withinthe space l0 increases, above a second predetermined value determined bythe difierential of operation of the thermostat the relay 26 isdeenergized to terminate operation of the furnace l4 and the supply ofheat to the space It].

The preheat coil on the present arrangement performs not only its usualfunction of changing the time of response of the thermostat but it alsoacts to compensate for voltage flu tuations by cooperation with the dualelement thermostat.

It is, of course, well-known that the preheat coil creates afalseambient about the thermostat and causes the latter to terminateoperation of the heating means sometime prior to the time that the roomtemperature reaches the value which it is desired to maintain therein.Thus, the furnace is operated intermittently and the overshooting oftemperature with the space l0 because of time'lag in the heating systemis avoided and better modulation of temperatures therein is obtained. Adetailed description of the operation of the preheat coil with the usualbimetallic thermostat may be obtained from Letters Patent No. 1,583,496granted to William L. Shafer on May 4, 1926.

When a single bimetallic element is used, an

infinitesimal change of temperature will operate to open the contacts.With an arrangement of the type I have described, a definite fixedtemperature differential is required to operate the thermostat becauseof the flow of current through the auxiliary bimetallic element 20. Uponinitial engagement of contacts 2| and 22, a flow of current through bothelements Hi and 20 results. The current flow through element I9 has anegligible effect on its temperature because of its larger crosssectional area and lower resistance but the current flowing throughelement 20 will heat that element and cause it to tend to move to theright and thus maintain a better contact with element 22. On asubsequent increase in temperaturethe contacts 2| and 22 will not bedisengaged immediately, but after a definite temperature rise thecontacts are opened and ele- Assuming now that the temperature difieren-3 tial necessary to open the contacts is 1 Fahren- 5 heit and thepreheat coil 24 is so constructed that when continuously energized itwill raise the; temperature therearound 12, the operation of E thedevice will be as follows; When the temperature in space I!) decreasesbelow a predetermined minimum value, contacts 2| and 22 engage to Eenergize relay 26 and the latter in turn energizes motor I6 by closureof switch 21. The furi nace is thereby rendered operative and suppliesvheat to the radiator Simultaneously, the preheat coil 24 is energizedand it starts to heat bimetallic element l9 locally. The action ofbimetallic element 20 is the same as described above. After thetemperature of bimetallic element I!) has been increased 1 as a resultof the joint effect of heat from radiator and the preheat coil24, thecontacts 2| and 22 will be disengaged. The operation just described willbe continued until the temperature within space I!) rises 1 above thepredetermined minimum value at which time bimetallic element 9 will nolonger efiect closure of contacts 2| and 22.

The operation above described will continue: so long as rated voltage issupplied from the source of energy l'l. However, it is very seldom thatthe source of supply in outlying distribution systems remains constant.Usually there is a considerable fluctuation in voltage and it is notunusual to have voltage fluctuations of plus or minus 10 per cent. Insuch event, the value of preheat would decrease to a value less than the1 necessary to effect opening of the contacts but at the same time thedecreased flow of current. through.element 20 would likewise result inthe requirement of a lesser temperature rise to cause opening of thecontacts. Thus, by so proportioni'zg the main and auxiliary elementsthat these oposite effects are equal, the objectionable ef- :cts ofvoltage fluctuations are avoided.

What I claim as new and desire to secure by etters Patent of the UnitedStates is:'

1. In combination, a source of heat exchange :edium, means fortransferring .said medium to desired region, means in said regioncontrolling Lid source, said means including thermal re- )onsive meansconsisting of two bimetallic strips 5 diflerent electrical resistancesand an electrical eater influencing one of said strips and conolied bysaid thermal responsive means.

2. In combination, a source of heat exchange iedium, means fortransferring said medium to desired region, electrical means forcontrolling 1e supply of said medium, a source of electrical nergy,thermal responsive means including a air of bimetallic strips ofdifferent cross seconal area fastened end to end for connecting ridelectrical means to said source of energy, nd an electrical heatercontrolled by said last ientioned means and influencing a predeteriinedone of said strips for changing .the time i control, said electricalheater and bimetallic trips being proportioned to compensate for theffect of voltage fluctuations thereupon.

3. In combination, a source of heat exchange .iedium, means fortransferring said medium to desired region, electrical means forcontrolling he supply of said medium, a source of electrical nergyfathermal responsive means including a air of bimetallic strips ofdifferent cross seclonal area fastened end to end for connecting aidelectrical means to said source of energy and n electrical heatercontrolled by and influencing aid last mentioned means, one of saidstrips having a relatively large cross sectional area and responsive tovariations in ambient temperature and the other a relatively smallercross sectional area and not responsive to variations in ambienttemperature but responsive to variations in temperature caused bycurrent flow therethrough, and said heater being in heat conductingrelationship with the strip of larger cross sectional area wherebyfluctuations in the voltage of said energy source are compensated for.

4. In combination, a space temperature controlling means having anelectrical control circuit, aspace temperature responsive switch forcontrolling said circuit and having an actuating element consisting oftwo oppositely acting bimetallic strips of different electricalresistance in said circuit, and an electrical heater influencing one ofsaid strips and controlled by said switch.

5. In combination, a circuit control switch having a bimetallicactuating element responsive to ambient temperature conditions andincluded in the circuit controlled by the switch, an auxiliarybimetallic element reversely mounted on "said first element to beincluded in circuit therewith and formed of high electrical resistancematerial with relatively small cross sectional area to provide responsethereof to the heating action of the current in the circuitsubstantially independently of ambient temperature, and an electricalheater influencing saidactuating element and connected to be energizedwhen the circuit cpntrolled by said switch is closed, said electricheater and said auxiliary bimetallic element being proportioned tocompensate for the effect of voltage fluctuation in said circuit.

FREDERICK W, HOI'I'ENRO'I'H. 3:.

